The Knitting Fiend

“How To Use the Magic Formula” (or How to Shape a Knitted Sleeve.)

The knitters on the knitting machines email list are discussing the “magic formula”. The topic comes up frequently, so I decided to write a “How to shape a sleeve” calculator. You can visit that web page and use its calculator whenever you are redesigning the lower portion of a sleeve. (Strangely enough, the sleeve shaping theory is can be applied when designing a halter top, and I’m knitting one right now! But, we’ll just pretend the formula is only used for sleeves.)

If you don’t want to understand, that’s ok. Once a calculator exists, it’s not absolutely necessary to understand. For today, don’t cross the line below. Just remember this discussion exists; return later if you ever decide you need to understand how to calculate shaping without using a program.

Those who want to cross the line, do so at your own risk!

Suppose I want to increase from 20 stitches to 44 stitches over 30 rows, and the piece is shaped like sleeve similar to the one illustrated to the right. Here’s how I would calculate the shaping:

• First, I’m an engineer by training, so I always draw a sketch before doing math. See the schematic.
• I want increase from 20 stitches at the cuff to 34 stitches at the bicep. That is a total of (34-20)=14 stitches, or 7 stitches on each side. I put a “7″ on either side of the schematic.
• I want the stitch increases to occur over 30 rows. To simplify shaping, I also want to make sure I only increase when the right side is facing (if I hand knit) or when the carriage is on the right (if I machine knit.) To force the decreases to occur only on odd numbered rows, I divide the number of rows by two and determine that 30 row / 2 = 15 pairs of rows. I labeled those values on the right hand side of the figure.
• Now, remember I want 7 increases? Notice, how I placed 7 red dots for the increases. Because this is a sleeve, I want to knit a few rows before the first increase and a few after the last one. So, I sprinkled the dots
  away from the edges. Examining the figure, I notice I have 8 =7+1 “regions” around the
  increases. I labeled the “8″ regions in green.
• Now, I’m going to figure out how many pairs of rows must be in each of those 8 regions.; To figure that out, I first divide 15 pairs/8 regions and round down. That results in 1 pairs of rows in each region. This means each region has at least 1 pair of rows in it, but some may need 2 (that’s one more than 1.).
• How many of the eight regions need 2 pairs of rows? Well, when I divided 15/8, I found 15/8= 1 plus 7 left over. So, 7 of the 8 regions need an extra pair of rows. Meanwhile 1 region (= 8-7) has only one pair
• That’s as far as the magic formula gets me. At this point, I, as the all powerful designer, must decide which 7 regions will have 2 pairs of rows and which has only 1 pair. I could sprinkle around the 7 regions and 1 region however you wanted. I decided to make the very first increase region have 1 pair of rows (that’s 2 rows), and all the rest have 2 pairs of rows (that’s 4 rows) . You’ll find the instructions below.
• Now, why don’t you repeat this exercise with the values you are going to
  knit? Compare your result to the one this page suggests. Notice that, since this is a program, I always put the regions with fewer rows first, and the ones with more rows
  later. You don’t need to do that. However, it has the advantage of making sure the sleeve is always at least as wide as necessary.

As an exercise, figure out how you would word my instructions. Then, visit the page with the geeky knitting calculator and see if you worded it the same way I did. (You probably didn’t. I word things to simplify slapping numbers into boxes, and avoid causing a program to say “do this, then repeat -1″ times, which people really, really don’t like.)

Of course, if you just remember the program exists, you can use it when you decide to redesign that sweater in Vogue Knitting. (Yes. I mean you Bevin; I just know you are a line crosser! )